1. Field of the Invention
The present invention relates to an image formation device equipped with a fixing apparatus which is employed in a copying device, printer or the like, which is structured to serve as an electrophotography system.
2. Description of the Related Art
Commonly, in an image formation device such as a copying device, a printer or the like that employs an electrophotography system, a photosensitive body formed in, for example, a drum shape is uniformly charged, the photosensitive body is exposed with light which is controlled in accordance with image information, and an electrostatic latent image is formed on the photosensitive body. Hence, this electrostatic latent image is made visible with toner (a toner image), and this toner image is transferred to recording paper and is fixed by a fixing apparatus, for image formation.
Among electrophotography-system image formation devices, there are color image formation devices which form full-color images. These color image formation devices are of, broadly speaking, a type which employs an intermediate transfer body and a type which does not employ an intermediate transfer body. An image formation device which employs an intermediate transfer body has the advantage, because toner images formed on the photosensitive body are temporarily primary-transferred onto the intermediate transfer body, of being able to implement primary-transfer without regard to the material of a recording medium, thus improving image quality of full-color images.
Further, among color image formation devices which employ an intermediate transfer body, there are devices of a “four-cycle” system and devices of a “tandem” system. A color image formation device of the four-color system primary-transfers toner images of each of the colors, such as yellow, magenta, cyan and black, or the like, which are formed sequentially on a single photosensitive body, onto an intermediate transfer body in a state in which the toner images are superposed with one another. The device then secondary-transfers the yellow, magenta, cyan and black (or whatever colors) toner images, which have been superposedly transferred onto the intermediate transfer body, onto a recording medium with a secondary transfer roller. Thus, a color image is formed.
On the other hand, a color image formation device of the tandem system forms toner images of mutually different colors, such as yellow, magenta, cyan and black, or the like, on plural (for example, four) photosensitive bodies and primary-transfers these toner images onto an intermediate transfer body in a state in which the toner images are superposed with one another. Then, the device secondary-transfers the yellow, magenta, cyan and black (or whatever colors) toner images, which have been superposedly transferred onto the intermediate transfer body, onto a recording medium with a secondary transfer roller. Thus, this structure forms a color image.
A fixing apparatus, which is employed in an image formation device of the various systems described above, passes recording paper bearing an unfixed toner image between, for example, a fixing roller and a pressure roller, and fixes the toner image to the recording paper by applying heat and pressure to the unfixed toner image.
With regard to fixing apparatuses for such electrophotography systems, schemes to raise fixing speed, improve image quality by preventing occurrences of fixing unevenness and paper creasing, reduce the size of a fixing apparatus, and shorten a warm-up time of a fixing apparatus, from room temperature up to a state in which fixing processing is possible, have been called for.
Accordingly, in response to such requests, realization of a fixing apparatus known as a free belt nip fuser has been attempted. A free belt nip fuser is a structure in which a fixing belt is slidably disposed on a surface of a pressure pad, which is fixed in place, a belt nipping width is broadened, and the fixing belt is pressed by a heating roller such that an exit side of the sheet is locally formed as an elastically deformed fixing surface.
At a free belt nip fuser with such a structure, a sheet to which a toner image has been transferred is nipped between the fixing belt and the heating roller, which is driven to rotate, and is operated to turn together with the fixing belt. At the same time, the toner image is fixed by a heating and pressing operation while the sheet is passing the fixing surface. Hence, the sheet is peeled from the fixing belt and ejected.
With this free belt nip fuser, it is possible to achieve an increase in nipping width of the belt, an increase in speed of the fixing process, and a reduction in size of the fixing apparatus. It is also possible to achieve a reduction in amounts of beat lost from the heating roller to the fixing belt and pressure pad side, a reduction in amounts of temperature lowering at a nipping region of the belt, an increase in efficiency of utilization of heat in fusing of the toner, an improvement in fixing characteristics of the toner and a shortening of warm-up times (see, for example, Japanese Patent No. 3,298,354).
At such a fixing apparatus, in order to carry out fixing processing by heating and pressing a sheet to which a toner image has been transferred while the sheet is being conveyed by the nipping region, the heating roller is heated to a high temperature which is required for fixing. Consequently, heat from the heating roller that has been heated to the high temperature is spread to the surroundings, hot air passes through the interior of a housing of an image formation device, inside which housing the fixing apparatus is disposed, and there is a risk of a developing apparatus, an exposure apparatus and so forth inside, the housing being heated to high temperatures and suffering adverse effects. Accordingly, image formation devices which are equipped with these fixing apparatuses commonly have structures in which an exhaust fan is provided at a vicinity in which the fixing apparatus is disposed and the exhaust fan forcibly exhausts hot air from an exhaust outlet, which is formed through the housing.
However, when hot air is forcibly exhausted from an exhaust outlet by an exhaust fan disposed near a fixing apparatus in this manner, there is a problem in that the hot air which is, being continuously exhausted in a certain direction from the exhaust outlet carries a bad odor. Thus, people who are stationed in a vicinity of the exhaust outlet near the fixing apparatus in the image formation device, people passing through this vicinity and the like experience unpleasant odors. Furthermore, there are problems in that, if an exhaust fan disposed near a fixing apparatus is continuously operated to forcibly exhaust hot air from an exhaust outlet, the air exhaust operation of the exhaust fan is accompanied by emissions of continuous noise. Moreover, amounts of energy consumed for continuously operating the exhaust fan are large, and the image formation device is increased in cost by an amount corresponding to the exhaust fan.